Antimatter comprises a positively charged electron (positron) and a negatively charged proton (antiproton). A positron is the anti-particle of an electron, and is an elementary particle having the same mass and the opposite charge as an electron. When positrons are implanted in a solid they are rapidly thermalized and annihilate with electrons. There are three known electrically neutral species of antimatter, one formed by combining equal numbers of positrons and antiprotons, one formed by combining equal numbers of protons and antiprotons, and positronium (Ps) which is formed from a mixture of electrons and positrons. Positronium has the lowest rest mass of any known atom. It is known that a positron and an electron briefly form an electron-positron pair (via coulomb forces) when the two particles meet in a molecular crystal or in an amorphous solid material, and then the pair annihilates. The positron-electron pair (positronium) behaves in a manner similar to a particle in a bound state.
Storage of lone positrons, however, is severely limited by the intrinsic inter-particle repulsive electric force, the so-called space charge force. From Coulomb's Law it is possible to compute that 1013 positrons at the center of a sphere of volume 100 cc (density=1×1011/cc) creates a static electric potential at the surface of the sphere equal to 500 kV. Thus an external potential of 500 kV is required to prevent a positron from escaping the sphere. These parameters represent severe limits to trapping of large numbers of positrons and the formation of stable quantities of positronium.
This annihilation problem may be circumvented by formation of the electrically neutral positronium atom. Unfortunately, the lifetime of positronium in its ground state is short, less than two hundred nanoseconds (ns). This is due to self-annihilation, wherein the positronium annihilates from the singlet state (with anti-parallel electron and positron spins) into two gamma rays, or from the triplet state (with parallel spins) into three gamma rays. From basic quantum statistics considerations, formation of positronium in vacuum is 75% triplet and 25% singlet. In addition, in the non-vacuum situation that is routinely encountered, the positron in the positronium atom can annihilate with a so-called bachelor electron that is attached to a neighboring, ordinary matter atom within the environment surrounding the positronium atom. This is called pick-off annihilation. If the positron and bachelor electron form a singlet state, annihilation takes place at a high rate (8 ns−1). This leads to a rapid depletion of triplet states. Depending upon the exact materials in the surrounding environment, and their density, in a matter of picoseconds (ps) to nanoseconds (ns) the fraction of spin triplet states can be reduced from 75% to 3% or less. Therefore, any device that claims to store Ps for periods of time significantly greater than a few hundred ns must create an environment that inhibits both positronium self and pick-off annihilations.
Positronium Formation, Orbits and Self-Annihilation
As will be understood by those skilled in the art, a complete description of the positronium (Ps) atom 2 requires a quantum mechanical treatment in which each quantum state requires specification of a four-fold set of quantum numbers. These include the principal quantum number n, the angular momentum quantum number l, measured in units of ℏ, or Planck's constant divided by 2π or, about 1.05×10−34 J-sec, the magnetic quantum number m, and the spin quantum number, +/−½. The relationship between n and l is l=0, 1, 2, 3, 4 . . . , or n−1, and the relationship between l and m is −l<m<+l. With these four quantum numbers a detailed description of the Ps quantum state can be constructed. The Correspondence Principle (CP) teaches that as n becomes large, quantum mechanical solutions to atomic and molecular problems can be viewed accurately from a classical viewpoint. As a consequence, the following description of the preferred embodiments of the invention will rely upon the CP, as appropriate, to simplify solutions to otherwise complicated problems.
Circular Rydberg States
The formation of Ps atom 2 typically starts with an electron 4, that is attached to an atom, interacting at a large distance with a positron 6. In order to conserve energy and momentum a third body, e.g., the atomic ion associated with electron 4, must participate in the interaction. The initial binding of electron 4 and positron 6 often takes place in a highly excited circular state (n˜100-200) commonly referred to in the art as a Rydberg state. When a positron possessing a large amount of angular momentum captures an electron so as to form a Ps atom, known physical laws of conservation of angular momentum require that the positron necessarily transfers its angular momentum to the newly formed Ps atom in the form of a large value of l, e.g., l˜n−1. This large value of l, along with specification of m, defines a circular orbit. Under normal physical conditions, this unstable Rydberg Ps atom 2 decays by spontaneous sequential emission of single photons (Δn=1) so as to decay in a stepwise fashion. The time required for the paired electron 4 and positron 6 to reach a ground state, from a circular orbit, and annihilate, in quantum mechanical terms is τA=1.08×10−10 n5.236 seconds. For example, if an extraordinarily long time on the atomic scale, is used, e.g., τA=1 day=8.64×104 seconds, then principal quantum number n=702, resulting in a radius r of the resulting circular Ps atom 2 of 0.1 n2 nanometers. Thus for n=702, r equals 49 micrometers (μm), forming an extraordinarily large atom. The binding energy E of this Ps atom is −6.8/n2 eV or −1.38×10−5 electron-Volts (eV). This energy, expressed in units of Kelvin temperature (K), is 0.17 K, or 0.05% of room temperature. To make long-term storage of Ps atoms practical storage devices and methods would have to be operated at this temperature or below. If not, the Ps atom is ionized by collisions with atoms in the surrounding medium. This is very often a difficult temperature regime requiring the implementation of very special and expensive techniques.
Known neutral atom traps have a complex implementation, limited efficiency, and limited mass storage capacity. U.S. Pat. Nos. 5,977,554 and 6,160,263, both entitled “Container for Transporting Antiprotons” issued on Nov. 2, 1999, and Dec. 12, 2000, respectively, to Gerald A. Smith et al., and U.S. Pat. Nos. 6,414,331 and 6,576,916, both entitled “Container for Transporting Antiprotons and Reaction Trap” issued on Jul. 2, 2002 and Jun. 10, 2003, to Gerald A. Smith et al., disclose a container for transporting antiprotons, including a dewar having an evacuated cavity and a cryogenically cold wall. A plurality of thermally conductive supports are disposed in thermal connection with the cold wall and extend into the cavity. An antiproton trap is mounted on the extending supports within the cavity. A scalable cavity access port selectively provides access to the cavity for selective introduction into and removal from the cavity of the antiprotons. The container is capable of confining and storing antiprotons while they are transported via conventional terrestrial or airborne methods to a location distant from their creation. An electric field is used to control the position of the antiprotons relative to the magnetic bottle that confines the antiprotons.
In U.S. Pat. No. 6,813,330, issued to Barker et al., a device is suggested for capturing and storing positronium that includes an antimatter trap having a three-dimensional or two-dimensional photonic band gap structure containing at least one cavity. The positronium atoms are stored in the cavity or in an array of cavities. The photonic band gap structure apparently blocks premature annihilation of the excited species by preventing decays to the ground state. Although, Barker et al., suggest that their device also blocks pickoff annihilation processes, no facility is taught for that effect.